This application relates to axial flow fans having forwardly skewed blades, particularly banded plastic fans such as those designed for automotive applications and for other air handling applications including computer cooling and heating/cooling of buildings.
In various applications, axial fans are designed to move airflow through adjacent heat exchangers or through air channels. Noise, strength, packaging (size) and efficiency (energy consumption) are important considerations in many axial fan applications.
In particular, it has been found that a fan whose blades are forwardly skewed (e.g., the mid-chord line and/or the leading edge of the fan's blades are curved in the direction of fan rotation) will exhibit significantly less noise, all other things being equal. See, Gray, U.S. Pat. No. 4,358,245. Gray '245 also teaches that it is useful in forwardly skewed blade designs to increase the blade angle with increasing radius.
Gray U.S. Pat. No. 4,569,631 discloses a fan having a forward skew at the blade tip and a rearward skew at the blade root so that the overall angular dislocation in the plane of rotation between the blade root and the blade tip is reduced, providing greater strength. The blade angle remains relatively constant at the blade tip.
Brackett et al. U.S. Pat. No. 4,900,229 discloses an axial flow fan having a blade with a sinusoidally shaped leading edge.
E.P. 0 168 594 discloses an axial fan with blades that have a forwardly curved leading edge.
U.S. Pat. No. 5,000,660 discloses an axial fan having multiple blades with different degrees of skew, either forward or back.
U.S. Pat. 4,791,520 discloses a forwardly skewed fan blade having a controlled trailing edge.
U.S. Pat. No. 4,981,461 discloses a fan having blades with an abrupt change in skew and a high forward skew at the blade tip.
McDonald, U.S. Pat. No. 3,285,501, discloses a centrifugal fan having vanes 30 positioned to produce an annular ring of spinning air around the inlet of the fan wheel.
White, U.S. Pat. No. 3,307,776, discloses a centrifugal fluid flow apparatus having guide vanes 16 to guide and stabilize leakage flow around the fan.
Murphy, U.S. Pat. No. 2,981,461, discloses a centrifugal fan which uses the flow of air off of the open outer edges of the blades as a volume control--i.e., outlet vortical flow rotating in the direction of fan rotation can be recirculated as secondary air into the rotor inlet to reduce net volume.
Kuroda et al., U.S. Pat. No. 4,432,699, discloses a centrifugal blower having hair-like elements 69 (FIG. 6) mounted in a wall of passage between the fan and an inlet shroud. The hair-like elements increase resistance to reduce recirculation.
Hauser, U.S. Pat. No. 4,357,914, discloses a cooling fan for use with a radiator having a baffle ring 11 to reduce recirculation.
Wood, U.S. Pat. No. 3,627,440, discloses a seal plate 30 for an inlet for a centrifugal fan to assist the boundary layer to distribute the inlet air uniformly.
Schwaebel, DEOS 24 62 465 discloses a compressor turbine having ribs in the gap between the rotor blade tips and the housing.
Bruno, DEOS 1 905 269 discloses an impeller having a seal between the neck ring of the impeller and the ventilator suction opening.
SU 918,559 discloses a centrifugal pump having flanges which engage ring-shaped projections of a seal ring.